Computer Science 2 is one of the core elements of any computer science program; however, there has been little progress towards the development of a concept inventory for this key introductory course for CS majors. Plans to address this gap using the Delphi method are presented. Instructors and researchers with knowledge and experience of CS2 are being recruited to help identify concepts from CS2 that are both important and challenging. These will then be distilled, through an iterative research methodology, to create a concept inventory that will undergo validity and reliability checking through large scale field testing, qualitative interview analysis and appropriate psychometric testing.